Metal matrix composite's (MMC's) have long been recognized as promising materials due to their combination of high strength and stiffness combined with low weight. MMC's typically include a metal matrix reinforced with fibers. Examples of metal matrix composites include aluminum matrix composite wires (e.g., silicon carbide, carbon, boron, or polycrystalline alpha alumina fibers in an aluminum matrix), titanium matrix composite tapes (e.g., silicon carbide fibers in a titanium matrix), and copper matrix composite tapes (e.g., silicon carbide fibers in a copper matrix).
The use of some metal matrix composite wires as a reinforcing member in bare overhead electrical power transmission cables is of particular interest. The need for new materials in such cables is driven by the need to increase the power transfer capacity of existing transmission infrastructure due to load growth and changes in power flow due to deregulation. Basic performance requirements for such new materials include corrosion resistance, environmental endurance (e.g., UV and moisture), resistance to loss of strength at elevated temperatures, and creep resistance.
Important properties for performance are elastic modulus, density, coefficient of thermal expansion, electrical conductivity, and strength. These properties are typically governed by the choice and purity of constituents (i.e., the metal matrix material and the fiber) in combination with the fiber volume fraction. Of these properties, emphasis has been placed on the development of wires made from fibers with high tensile strength and stiffness.
The presence of imperfections in the wire such as intermetallic phases, porosity as a result, for example, of shrinkage or internal gas (e.g., hydrogen or water vapor) voids, and particularly dry (i.e., uncoated) fiber, are known to decrease properties such as strength the of the wire. These imperfections can result from impurities in constituents (i.e., material of the metal matrix and the fiber), incompatibility of constituents, as well as incomplete infiltration of the matrix material into the fibers.
There is a need for substantially continuous metal matrix composite wire with consistently good mechanical properties.